ADDIS ABABA, July 9 (Reuters) - Yemeni authorities have handed over to Ethiopia an opposition official who had been sentenced to death in absentia on charges of plotting to overthrow the Addis Ababa government, state media reported on Wednesday.

Andargachew Tsige, a secretary-general of the Ginbot 7 group, was among 20 opposition figures and journalists charged with conspiring with rebels, plotting attacks and attempting to topple the government.

Andargachew, who also holds British citizenship, was sentenced to death in 2009 in absentia. Another trial handed him life behind bars three years later.

Ethiopia's intelligence agency tipped off its Yemeni counterpart of his impending arrival in Sanaa in transit from Dubai to Eritrea, the agency said in a statement reported by state media.

He "was then handed back to Ethiopia by Yemeni officials the same day," the National Intelligence and Security Service (NISS) said.

It is the first time that Addis Ababa has acknowledged his detention. Rights groups had reported his disappearance in Sanaa last week.

"Given that Mr Tsige is a political activist who has been tried and sentenced to death in his absence, and given the regularity with which political opponents are tortured, there is a real danger that Mr Tsige's life could be at risk," said Allan Hogarth, Amnesty International UK's Head of Policy and Government Affairs.

Rights groups say Ethiopia regularly uses security concerns as an excuse to crack down on dissent and media freedom. The Ethiopian government denies the charge.

Ginbot 7 was formed by opposition figures who took part in disputed polls in 2005 and subsequently fled into exile and announced they advocated armed struggle against the government.

(Reporting by Aaron Maasho; Editing by George Obulutsa and Angus MacSwan)